Low Cost Amorphous Steel

ABSTRACT

Design and fabrication processes and compositions for iron-based bulk metallic glass materials or amorphous steels. Examples of bulk metallic glasses based on the described compositions may contain approximately 59 to 70 atomic percent of iron, which is allowed with approximately 10 to 20 atomic percent of metalloid elements and approximately 10 to 25 atomic percent of refractory metals. The amorphous steels may exhibit X-ray diffraction patterns as shown in FIG.  1.  The compositions can be designed using theoretical calculations of the liquidus temperature to have substantial amounts of refractory metals, while still maintaining a depressed liquidus temperature. The alloying elements are molybdenum, tungsten, chromium, boron, and carbon. Some of the alloys are ferromagnetic at room temperature, while others are non-ferromagnetic. These amorphous steels have increased specific strengths and corrosion resistance compared to conventional high strength steels.

This application claims the priority of U.S. Provisional PatentApplication No. 60/613,780 entitled “LOW COST AMORPHOUS STEEL” and filedSep. 27, 2004.

BACKGROUND

This application relates to compositions of amorphous metallic materialsand bulk metallic glasses (BMGs).

Amorphous metallic materials made of multiple components are amorphouswith a non-crystalline structure and are also known as “metallic glass”materials. Such materials are very different in structure and behaviorsfrom many metallic materials with crystalline structures. Notably, anamorphous metallic material is usually stronger than a crystalline alloyof the same or similar composition. Bulk metallic glasses are a specifictype of amorphous materials or metallic glass made directly from theliquid state without any crystalline phase and exhibit slow criticalcooling rates, e.g., less than 100 K/s, high material strength and highresistance to corrosion. Bulk metallic glasses may be produced byvarious processes, e.g., rapid solidification of molten alloys at a ratethat the atoms of the multiple components do not have sufficient time toalign and form crystalline structures. Alloys with high amorphousformability can be cooled at slower rates and thus be made into largervolumes. The amorphous formability of an alloy can be described by itsthermal characteristics, namely the relationship between its glasstransition temperature and its crystallization temperature, and by thedifference between its liquidus temperature and its ideal solutionmelting temperature. Amorphous formability increases when the differencebetween the glass transition temperature and crystallization temperatureincreases, and when the difference between its liquidus temperature andideal solution melting temperature increases.

Various known iron-based amorphous alloy compositions suitable formaking non-bulk metallic glasses) have relatively limited amorphousformability and are used for various applications, such as transformers,sensor applications, and magnetic recording heads and devices. These andother applications have limited demands on the sizes and volumes of theamorphous alloys, which need to be produced. By contrast, iron-basedbulk metallic glasses can be formulated to be fabricated at slowercritical cooling rates, allowing thicker sections or more complex shapesto be formed. These Fe-based BMGs can have strength and hardness farexceeding conventional high strength materials with crystallinestructures and thus can be used as structural materials in applicationsthat demand high strength and hardness or enhanced formability.

Some iron-based bulk metallic glasses have been made using ironconcentrations ranging from 50 to 70 atomic percent. Metalloid elements,such as carbon, boron, or phosphorous, have been used in combinationwith refractory metals to form bulk amorphous alloys. The alloys can beproduced into volumes ranging from millimeter sized sheets or cylinders.A reduced glass transition temperature on the order of 0.6 and asupercooled liquid region greater than approximately 20K indicates highamorphous formability in Fe-based alloys.

SUMMARY

This application describes compositions of and techniques for designingand manufacturing iron-based amorphous steel alloys with a significantlyhigh iron content and high glass formability that are suitable forforming bulk metallic glasses. For example, a composition suitable forbulk metallic glasses described in this application may include 59 to 70atomic percent of iron, 10 to 20 atomic percent of metalloid elements,and 10 to 25 atomic percent of refractory metals, where the iron,metalloid elements and refractory metals are alloyed with one another toform an amorphous phase material. One exemplary formulation foriron-based metallic glass materials isFe_(78-a-b-c)C_(d)B_(e)Cr_(a)Mo_(b)W_(c)where (a+b+c)≦17, ‘a’ ranges from 0 to 10 (e.g., 2 to 10), ‘b’ from 2 to8, ‘c’ from 0 to 6, ‘d’ from 10 to 20, and ‘e’ from 3 to 10. The valuesof a, b, c, d, and e are selected so that the atomic percent of ironexceeds 59 atomic %. One specific example isFe_(78-a-b-c)C₁₂B₁₀Cr_(a)Mo_(b)W_(c).

Bulk metallic glass materials based on the above formulation may bedesigned by computing the liquidus temperatures based upon theconcentrations of alloying elements and optimizing the compositions.This method determines alloys with high glass formability by usingtheoretical phase diagram calculations of multi component alloys.

As another example, this application describes a composite material thatincludes 59 to 70 atomic percent of iron, 10 to 20 atomic percent of aplurality metalloid elements, and 10 to 25 atomic percent of a pluralityof refractory metals. The iron, metalloid elements and refractory metalsare alloyed with one another to form an amorphous phase material.

A process for producing a bulk metallic glass based on a compositiondisclosed here is described as an example. First, a mixture of thecomponents including iron, refractory metals, carbon and boron is meltedinto an ingot (e.g., using an arc melting process). The molten finalingot is solidified to form a bulk amorphous metallic material. Thesolidification may be conducted rapidly using a chill casting technique.This fabrication process can be used to make Fe-based alloys intoamorphous samples with 0.5 mm in thickness in its minimum dimension.This process can also be used to produce, among other compositions, asteel of Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂ with a high iron content and a largesupercooled liquid region greater than about 50K.

These and other compositions and their properties and fabrications aredescribed in the attached drawings, the detailed description, and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows measured X-ray diffraction patterns showing amorphousstructures of a) Fe₆₀C₁₅B₈Mo₁₀Cr₄W₃, b) Fe₆₀C₁₈B₅Mo₁₀Cr₄W₃, c)Fe₅₉C₁₂B₁₀Mo₁₁Cr₅W₃, d) Fe₆₁C₁₂B₁₀Mo₁₀Cr₄W₃, e) Fe₆₁C₁₂B₇Mo₁₁Cr₃W₃,Fe₆₈C₁₂B₃Mo₁₀Cr₅W₂, f) Fe₆₈C₁₀B₁₀C₄Mo₆W₂, and g) Fe₆₄C₁₀B₈Mo₁₁Cr₄W₃,Fe₆₈C₁₀B₈Mo₁₁W₃, where the vertical axis is the measured strength of thediffraction signal and the horizontal axis is the measured angle whichis twice of the diffraction angle.

FIG. 2 shows the measured X-ray diffraction pattern showing theamorphous structure of (Fe₆₈C₁₀B₁₀Cr₄Mo₆W₂)₉₈Y₂.

FIG. 3 shows the measured X-ray diffraction pattern showing theamorphous structure of (Fe₅₇C₁₀B₁₀Cr₁₃Mo₇W₃)₉₈Y₂.

FIG. 4 shows the measured X-ray diffraction pattern showing theamorphous structure of Fe₆₁C₁₂B₁₀Cr₄Mo₁₀W₃.

FIG. 5 shows the measured X-ray diffraction pattern showing theamorphous structure of Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂.

FIG. 6 shows thermal mechanical analysis (TMA) results forFe₆₈C₁₂B₃Cr₅Mo₁₀W₂ where the glass transition temperature Tg isindicated by an arrow.

FIG. 7 shows differential thermal analysis (DTA) results forFe₆₈C₁₂B₃Cr₅Mo₁₀W₂ where glass transition and crystallizationtemperatures are indicated by arrows.

DETAILED DESCRIPTION

Designing of bulk metallic glass compositions having multiple elementswith desired material properties is technically difficult in partbecause the complexities of the interactions and effects of thedifferent elements. In such a complex material, a change in any aspectof the composition, such as the quantity of one element or asubstitution of one element with another element, may significantlyaffect the property of the final metallic glass material. Due to suchcomplexity, many known metallic glass compositions are results of trialand error. The Fe-based metallic glass compositions described in thisapplication were designed based on a systematic approach to selection ofmetalloid elements and refractory metal elements in combinations withiron to search for compositions with high glass formability representedby a large difference between a low glass transition temperature and ahigh crystallization temperature and a large difference between theliquidus temperature and the ideal solution melting temperature whichthe weighted average of the melting temperatures of different elementsin the mixture.

Under this approach to designing a specific bulk metallic glass, theliquidus temperatures are calculated based upon the concentrations ofdifferent alloying elements selected as the constituents of the bulkmetallic glass. The compositions are then optimized based on therespective resulting liquidus temperatures. The concentrations ofrefractory metal elements such as molybdenum and chromium added to theFe-based alloy can also be optimized such that the final alloy has 1) ahigh or maximum viscosity due to high concentrations of added refractorymetals, and 2) a low or minimum liquidus temperature. The compositionsare selected to achieve low liquidus temperatures and high idealsolution melting temperatures so that a candidate composition has alarge difference between the liquidus temperature and the ideal solutionmelting temperature. Such candidate compositions can maintain theirliquidus phase over a large temperature range within which a relativelyslow cooling process can be used to achieve the amorphous phase in abulk material. Among the candidate compositions with a large differencebetween the liquidus temperature and the ideal solution meltingtemperature, compositions with a large difference between a low glasstransition temperature and a high crystallization temperature arefurther identified and selected as candidates for the final metallicglass composition. This numerical and systematic design approach workswell in predicting the compositions of existing amorphous alloys and wasused to design the compositions of the examples described below.

One application of the above design approach is metallic glasscompositions based on the metal iron, which is relatively inexpensiveand widely available. Such iron-based metallic glass materials can bedesigned to achieve good glass formability at a reasonably low price toallow for mass production and uses in a wide variety of applications.The compositions of iron-rich amorphous alloys described here can beused to reach an amorphous state under a modest cooling rate, thusforming bulk metallic glass materials. Several examples of such bulkmetallic glasses described here have a content of iron of approximatelyfrom 59 to 70 atomic percent and are also referred to as amorphoussteels. In these examples, the iron is further alloyed with 10 to 20atomic percent metalloid elements and 10 to 25 percent refractorymetals. The compositions are chosen using theoretical calculations ofthe liquidus temperature. The alloys are designed to have a sufficientamount of refractory metals to stabilize the amorphous structure, whilestill maintaining a depressed liquidus temperature. In someimplementations, the principal alloying elements may be molybdenum,tungsten, chromium, boron, and carbon. Some of the resulting alloys areferromagnetic at the room temperature, while others arenon-ferromagnetic. These amorphous steels have increased specificstrengths and corrosion resistance compared to conventional highstrength steels. The amorphous structure of these alloys imparts uniquephysical and mechanical properties to these alloys, which are notobtained in their crystalline alloy forms.

Notably, the compositions described here have a higher Fe content thanother Fe-based bulk metallic glass materials and do not use expensivealloying elements found in other Fe-based bulk metallic glass materialsto make the material amorphous under slow cooling conditions. Thecompositions of the present amorphous steels are significantly closer tostandard steel alloy compositions than other Fe-based bulk metallicglasses and thus are much more attractive to scale up production byusing various steel production techniques, processes and equipmentincluding existing techniques, processes and equipment. In comparison,various commercial bulk metallic glasses use Zr-based materials andtherefore are expensive to produce. The present compositions use iron,one of the cheapest and widely available metallic elements, as a majorcomponent and thus significantly reduce the cost of the materials.

One formulation of the present compositions can be expressed asFe_(78-a-b-c)C_(d)B_(e)Cr_(a)Mo_(b)W_(c),where the subscript parameters represent the relative atomic % of thedifferent elements. Based on the above described systematic designapproach, the relative quantities of the elements are limited by thefollowing conditions: (a+b+c)≦17; ‘a’ ranges from 0 to 10; ‘b’ from 2 to8; ‘c’ from 0 to 6; ‘a’ from 10 to 20; and ‘e’ from 3 to 10. Inaddition, the values of a, b, c, d, and e are selected so that theatomic percent of iron exceeds 59 atomic %. One amorphous material basedon this composition is Fe_(78-a-b-c)C₁₂B₁₀Cr_(a)Mo_(b)W_(c) for d=12 ande=10.

The alloys based on the above compositions may be produced by meltingmixtures of high purity elements. For example, the melting may beperformed in an arc furnace under an argon atmosphere. The alloy ingotis fabricated from iron as the main metal element, refractory elementssuch as Cr, W, and Mo, and metalloid elements such as carbon and boron.Specific quantities of these elements are selected based on the aboveprescription. The mixture of these elements with predetermined relativequantities may be melted together to form an ingot by, e.g., using arcmelting and other meting methods. The ingot is re-melted several timesto ensure homogeneity of the ingot and then cast into a chilled castingmold to produce a desired shape in an amorphous structure. The meltingmay be performed in an electric furnace, an induction-melting furnace,or any other melting technique that allows the elements in theabove-described compositions to be melted together. The heat for themelting may generate from various processes such as induction heating,furnace heating, or arc melting.

For example, the arc melting method was used to successfully produce thefollowing bulk metallic glass material samples with dimensions of atleast of 0.635 mm: Fe₆₈C₁₀B₁₀Cr₄Mo₆W₂Y₂, Fe₅₇C₁₀B₁₀Cr₁₃Mo₇W₃Y₂,Fe₆₁C₁₂B₁₀Cr₄Mo₁₀W₃, Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂, Fe₆₀C₁₅B₈Mo₁₀Cr₄W₃,Fe₆₀C₁₈B₅Mo₁₀Cr₄W₃, Fe₆₁C₁₂B₇Mo₁₁Cr₅W₄, Fe₆₁C₁₂B₁₀Mo₁₁Cr₃W₃,Fe₆₄C₁₀B₈Mo₁₁Cr₄W₃, and Fe₆₈C₁₀B₈Mo₁₁W₃. The samples were suction castinto a copper sleeve. Two sleeves of different thicknesses of 0.025″ and0.050″ were used. The amorphous nature of the cast alloys was verifiedusing X-ray diffraction. Thermal properties were obtained using adifferential thermal analyzer (DTA), a differential scanning calorimeter(DSC), and a thermal mechanical analyzer (TMA). Two classes of iron-richamorphous steels were produced; one class contains yttrium, and theother lacks yttrium. The alloys produced without the use of yttriumrepresent the optimum alloys in terms of their low costmanufacturability. In addition, these alloys are composed of elementsthat are relatively resistant to oxidation, further increasing theirmanufacture potential.

FIGS. 1 through 7 show various measured results of these samples. FIGS.1 through 5 are measured X-ray diffraction patterns showing amorphousstructures of the samples. FIG. 6 is measured TMA data for the samplewith a composition of Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂ where the vertical axis is theTMA probe position and the location where the probe falls down is usedas a measure of the glass transition temperature Tg. FIG. 7 showsdifferential thermal analysis (DTA) results for Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂ wherethe vertical axis is the heat flow used during the measurement. Thesharp transitions in DTA indicate when reactions occur, eitherendotherms or exotherms, indicative of crystallization, or melting, andeven the very small transition at the start reflecting the glasstransition. The specific DTA measurement in FIG. 7 shows the differencebetween the glass transition temperature (Tg) and the crystallizationtemperature (T×1) to be in excess of 50K, which is an indicator of agood glass forming ability.

The compositions of amorphous steel described here have higher levels ofiron in combination with low cost refractory metals and metalloidelements than various amorphous steels made by others. Therefore, theapplications of such high iron content amorphous steels are morefavorable to replace conventional high strength structural steels thanother amorphous steels. In particular, the composition ofFe₆₈C₁₂B₃Cr₅Mo₁₀W₂ has a high iron content of 68 atomic % and uses lowcost alloying elements of C, B, Cr, Mo and W to exhibit a largesupercooled liquid region, greater than approximately 50K. Therefore,this composition is suitable for bulk production for industrialapplications.

The Fe-rich materials based on the present compositions may be used in awide range of applications. The relatively high amorphous formability ofthese materials makes them desirable materials for a wide range ofapplications including but not limited to sporting goods such as tennisrackets reinforcements, skis, baseball bats, golf club heads, consumerand other electronics such as device cases, antennas, and thermalsolutions for high-strength, light-weight, components and parts used inmobile devices such as notebook computers, cell phones, portable PDA's,MP3 players, portable memory devices, multimedia players, components andparts used in avionics devices, and automotive parts and devices. TheFe-rich materials based on the present compositions may also be used aslow cost alternatives to titanium and other specialty alloys in variousaerospace, industrial, and automotive applications such as springs andactuators, and various corrosion resistant applications. In addition,the compositions may also be used to form non-ferromagnetic structuralmaterials in military applications for avoiding magnetic triggering ofmines. Furthermore, the present compositions may be used for biomedicalimplants, transformer cores, etc. Many other structural materialapplications are certainly possible.

In summary, only a few implementations are disclosed. However, it isunderstood that variations and enhancements may be made.

1. A composite material, comprising a plurality of components definedby:Fe_(78-a-b-c)C_(d)B_(e)Cr_(a)Mo_(b)W_(c) wherein (a+b+c)≦17, a rangesfrom 0 to 10, b from 2 to 8, c from 0 to 6, d from 10 to 20, and e from3 to 10 and wherein values of a, b, c, d and e are selected so that theatomic percent of iron exceeds 59 atomic %.
 2. The material as in claim1, further comprising Y and wherein a composition of the components isFe₆₈C₁₀B₁₀Cr₄Mo₆W₂Y₂.
 3. The material as in claim 1, further comprisingY and wherein a composition of the components is Fe₅₇C₁₀B₁₀Cr₁₃Mo₇W₃Y₂.4. The material as in claim 1, wherein a composition of the componentsis Fe₆₁C₁₂B₁₀Cr₄Mo₁₀W₃.
 5. The material as in claim 1, wherein acomposition of the components is Fe₆₈C₁₂B₃Cr₅Mo₁₀W₂.
 6. The material asin claim 1, wherein a composition of the components isFe₆₀C₁₅B₈Mo₁₀Cr₄W₃.
 7. The material in claim 1, wherein a composition ofthe components is Fe₆₀C₁₈B₅Mo₁₀Cr₄W₃.
 8. The material as in claim 1,wherein a composition of the components is Fe₆₁C₁₂B₇Mo₁₁Cr₅W₄.
 9. Thematerial as in claim 1, wherein a composition of the components isFe₆₁C₁₂B₁₀Mo₁₁Cr₃W₃.
 10. The material in claim 1, wherein a compositionof the components is Fe₆₄C₁₀B₈Mo₁₁Cr₄W₃.
 11. The material in claim 1,wherein a composition of the components is Fe₆₈C₁₀B₈Mo₁₁Cr₄W₃.
 12. Thematerial in claim 1, wherein a composition of the components isFe₅₉C₁₂B₁₀Mo₁₁Cr₅W₃.
 13. The material in claim 1, wherein a compositionof the components is Fe₆₁C₁₂B₁₀Mo₁₀Cr₄W₃.
 14. The material in claim 1,wherein a composition of the components is Fe₆₈C₁₀B₁₀Cr₄Mo₆W₂.
 15. Thematerial in claim 1, wherein a composition of the components isFe_(78-a-b-c)C₁₂B₁₀Cr_(a)Mo_(b)W_(c).
 16. A method for producing amaterial in claim 1, comprising: melting a mixture of the componentsinto an ingot; re-melting the ingot to produce a homogeneous moltenalloy; and solidifying the molten ingot to form a bulk amorphousmaterial.
 17. The method in claim 16, wherein an arc melting process isused to perform the melting.
 18. The method in claim 16, wherein aninduction melting process is used to perform the melting.
 19. Acomposite material, comprising: 59 to 70 atomic percent of iron; 10 to20 atomic percent of a plurality metalloid elements; and 10 to 25 atomicpercent of a plurality of refractory metals; wherein the iron, metalloidelements and refractory metals are alloyed with one another to form anamorphous phase material.
 20. The material as in claim 19, furthercomprising yttrium which is alloyed with the iron, metalloid elementsand refractory metals.
 21. The material as in claim 19, wherein themetalloid elements comprise C and B.
 22. The material as in claim 19,wherein the refractory elements comprise Cr, W and Mo.